Access network multi-homing is an existing technique in which an access network connects to multiple Internet Service Providers (ISPs) simultaneously in order to increase Internet connectivity bandwidth and to increase robustness to ISP failures. Traditionally, there have been two principal approaches for access network multi-homing. One is to advertise the addressing space of a multi-homed access network independently of each of its ISPs' addressing space in the global routing system, thus adding a separate routing table entry for the access network. The other approach is to let hosts select an ISP by enabling them to dynamically switch between IP addresses from ISP-dependent addressing spaces. Each addressing space is then advertised to the global routing system as part of the respective ISP's addressing space.
A third, more recent, approach to access multi-homing provides a level of indirection between the addressing space that access networks use internally and the addressing space that is used for carrying packets through transit space. Some indirection techniques require an address space mapping at the border of every access network. Other indirection techniques require only multi-homed access networks to provide a mapping on their border and to also subscribe to a (reverse) mapping that takes place at an indirection point somewhere in transit space.
All of these approaches lack at least one of the following desired properties:
1. Global routing table preservation. The global routing table should grow linearly with respect to the number of ISPs rather than linearly with respect to the number of access networks.
2. Traffic engineering. An access network should be able to force ingress and egress traffic to pass via one particular ISP of the ISPs with which it multi-homes.
3. Host preferences. A host should still be able to suggest to the access network, an ISP of its own choice that it would prefer its traffic to pass through.
4. ISP changes. It should be possible to quickly reroute traffic, in both directions, via an alternative ISP.
5. Network reconfiguration costs. An access network operator should be able to change its set of ISPs without costly reconfiguration of network devices.
6. Routing performance. Traffic characteristics such as packet propagation latencies, packet loss probabilities, or jitter should not change.
7. Transition. There should be a transition path for incremental deployment, which allows upgraded parts of the Internet to communicate with legacy parts.
8. Incentives for deployment. Deployment of a technique should yield direct benefits to those entities investing in the deployment.
9. Integrability. Where possible, a technique for access network multi-homing should be integrable with mobility techniques and, in the long run, possibly also host identity techniques.
The technique of advertising access networks' addressing spaces separately in the global routing system fails to preserve the global routing table, and does not enable hosts to express a preference with respect to an ISP for their traffic. Giving hosts the ultimate decision on which ISP their traffic is routed through, in turn, conflicts with the traffic engineering strategies of access networks. Indirection techniques that require mappings at the border of every access network have disadvantages regarding transition paths and deployment incentives. Indirection techniques also face unanswered questions with respect to how mappings can be maintained efficiently, or how they can be updated rapidly to support access networks in switching to an alternative ISP. On the other hand, indirection techniques that use an indirection point somewhere in transit space incur adverse impacts on routing performance.